1. Field of the Invention
The present invention relates to a filter for metal hot melt which is suitable for filtrating impurities (debris) contained in metal hot melt, and particularly in aluminum hot melt.
2. Description of the Related Art
Sheet metal or foil has been previously produced by rolling an ingot into which metal hot melt is cast. If the ingot is contaminated by solid impurities such as minute fragments of metal oxides or refractories contained in metal hot melt, pinholes or surface defects may arise in the sheet or foil during the rolling of the ingot when manufacturing such products. The prevention of these defects requires the removal of solid impurities contained in the hot melt. Accordingly, conventional means such as glass cloth, alumina balls, ceramic form, and the like have been used as filters for filtrating hot melt.
However, although glass cloth is inexpensive, it tends to be readily choked up, and alumina balls have inaccurate filterability since impurities which were once caught in the filter readily flowed out. Ceramic form has pores with a large diameter, whereby minute impurities are insufficiently filtrated.
Therefore, a cylindrical porous filter such as disclosed in Japanese Patent Publication No. 52-22327 has been used lately. The filter has numerous minute consecutive pores formed between aggregate particles of silicon carbide, silicon nitride, alumina, or like materials which are bound to each other by an inorganic binder. This filter is superior to the above-mentioned filters in filtrating: clogging is prevented for a long period; impurities which are once caught can not flow out; a suitable pore diameter can be set to filtrate minute impurities.
However, nowadays there is an increasing need for a more effective filter for metal hot melt in the industry that manufactures substrates for memory disks used for computer memory. In such fields, even a cylindrical filter mentioned above does not have stable filterability due to its inconsistent quality and changes of the hot melt filtering conditions. Therefore, its reliability for catching impurities (debris) is not sufficient.